FWIW, fellow Early S registry member Chuck Miller & I would both agree. Both of us experienced flat spots with 2 in 2 out mufflers. Flat spots vanished when we went back to stock. The funny aside is that I gave my 2 in 2 out to a guy with a carbed 2.2 911T, and he claimed a performance improvement. That not documented, so I'm suspecting he just enjoyed the sound...
